On Tue, 29 Sept 2026 at 10:24, Adam Thompson via tz <[email protected]> wrote:
> While CDT and EST are the same thing mathematically, they are vastly > different things linguistically, legally, socially and politically. > Our approach here mirrors that which we've taken with the other provinces and territories which have ended seasonal time changes this year, and reflects a long-standing norm to interpret year-round time standards as standard time. This fits legally as well, since the Act does not institute "permanent DST", but rather redefines a year-round standard time one hour ahead of the previous standard time. Additionally, EST matches existing and recent usage for year-round UTC−5 in North America — currently in Atikokan, Ontario as well as in Cancún and Panama, but also in Indiana until 2006. >From <theory.html>, *“Use abbreviations that are in common use among > English-speakers […] CST/CDT/CWT/CPT Central [North America] […]”*. > *CDT *is the abbreviation in common use here in English; I have never > heard anyone refer to local Manitoba time as EST during CDT. While that is a data point, seasonal usage of such nomenclature from before this change is not, itself, hard evidence of continued usage after the change. Specifically, the language you cite from theory.html exists to remind us of our archival role, and that we should follow *de facto* usage for abbreviations in a way that tends to lag, not lead. Amidst both changing and unchanging neighbors, though, predicting how future usage will shake out unavoidably results in circular logic either way, so we look in the meantime to both recent and nearby practice as laid out above, which is how we've landed on MST/CST/EST for now instead of PDT/MDT/CDT. There was similar discussion regarding British Columbia which has recently adopted a preferred abbreviation for official/governmental use, but for which it's also too early to tell what the general public will use: https://lists.iana.org/hyperkitty/list/[email protected]/thread/Y432QXUMA5SJDZTRLBPCQSGUK6SYCUEV/#YUJ6ZLVLY6TECPX7ZPXO2R64S2IVG3UD In short, it's very early days for all of these abbreviations. That said, the social difference between what is mathematically a zone shift and what is culturally less so is certainly acknowledged. It absolutely DOES strain the traditional nomenclature to extend "Mountain" to the west coast, "Central" into the mountains, and "Eastern" into the central plains. So, as described in the BC thread, we will continue to monitor the abbreviations that become adopted by the general public as the effects of these changes percolate throughout the affected regions and their neighbors. > it’ll be a new time zone “Manitoba Standard Time”, which *also* does not > abbreviate to EST, it will abbreviate – with the force of law – to “MBT”. > Even if the new province-specific abbreviations do end up catching on, they would still create new problems for areas near provincial and zonal boundaries: Areas in southeastern BC which have chosen year-round UTC−6 remain covered by America/Edmonton, but should a location outside of Alberta get the abbreviation "ABT"? Much of the rest of BC is covered by America/Vancouver where the official guidance for UTC−7 is now "PCT", but this is identical to Creston and Fort Nelson's "MST" which continue to use that designation according to that same guidance, as well as to the "MST" we've used for Yukon since 2020 without issue. Likewise, using "MBT" for areas in northwestern Ontario that end up following Winnipeg's clocks could equally be a non-starter. So, since there is a lot we still don't know, this is why we haven't deviated from the traditional nomenclature for the time being. -- Tim Parenti >
